Currently, liquid crystal display devices (hereinafter, also referred to simply as “LCDs”) are used for various applications. In general LCDs, one pixel is formed of three picture elements respectively for providing display in red, green and blue, which are three primary colors of light, and thus color display can be provided.
However, conventional LCDs have a problem that the range of colors which can be displayed (referred to as the “color reproduction range”) is narrow. FIG. 18 shows a color reproduction range of a conventional LCD which provides display using the three primary colors. FIG. 18 is an xy chromaticity diagram of an XYZ color representation system, in which a triangle having, as apexes, three points corresponding to the three primary colors of red, green and blue represents the color reproduction range. In the figure, colors of various objects existent in the natural world which were found by Pointer are plotted with “x” (see Non-patent Document No. 1). As understood from FIG. 18, there are colors of objects which are not encompassed in the color reproduction range. An LCD providing display using the three primary colors cannot display a part of the colors of objects.
In order to enlarge the color reproduction range of LCDs, techniques for increasing the number of primary colors usable for display to four or greater have been proposed.
For example, as shown in FIG. 19, Patent Document 1 discloses an LCD 800 in which one pixel P is formed of six picture elements R, G, B, Ye, C and M respectively for displaying red, green, blue, yellow, cyan and magenta. FIG. 20 shows the color reproduction range of the LCD 800. As shown in FIG. 20, the color reproduction range represented by a hexagon having, as apexes, six points corresponding to six primary colors encompasses substantially all the colors of objects. In this way, the color reproduction range can be enlarged by increasing the number of primary colors.
Patent Document 1 also discloses an LCD in which one pixel is formed of four picture elements for displaying red, green blue and yellow, and an LCD in which one pixel is formed of five picture elements for displaying red, green blue, yellow and cyan. By using four or more primary colors, an LCD can enlarge the color reproduction range as compared to the conventional LCD providing display using the three primary colors. In this specification, LCDs providing display using four or more primary colors will be collectively referred to as a “multiple primary color liquid crystal display device (or multiple primary color LCD)”.
On the other hand, LCDs capable of providing high quality display both outdoors and indoors have been proposed (for example, Patent Document 2). Such LCDs are referred to as “transreflective LCDS” and have a reflection area for providing display in a reflection mode and a transmission area for providing display in a transmission mode in one pixel.
FIG. 21 shows an example of a transreflective LCD. An LCD 900 shown in FIG. 21 has a pixel defined by three picture elements R, G and B respectively for displaying red, green and blue.
The three picture elements R, G and B each have a transmission area Tr for providing display in a transmission mode and a reflection area Rf (hatched in the figure) for providing display in a reflection mode. Typically, the reflection area Rf accommodates a reflective electrode formed of a conductive material having a high light reflectance such as aluminum or the like. By contrast, the transmission area Tr accommodates a transmissive electrode formed of a conductive material having a high light transmittance such as ITO or the like.
The area size ratio of the transmission area Tr and the reflection area Rf is determined based on which mode of display, i.e., the transmission mode or the reflection mode, is prioritized and to which degree. As the transmission mode of display is more prioritized, the area size of the transmission area Tr is set to be larger; whereas as the reflection mode of display is more prioritized, the area size of the reflection area Rf is set to be larger. From the viewpoint of improving the indoor display quality, the transmission mode of display needs to be prioritized and the area size of the transmission area is set to be larger.
The reflective electrode and the transmissive electrode are switched to each other by a thin film transistor 11 provided in each picture element. The thin film transistor 11 is supplied with a scanning signal from a scanning line 12 and is supplied with a video signal from a signal line 13. A storage capacitance line 14 is provided so as to extend parallel to the scanning line 12. In an area outside the picture elements, a lattice-shaped (or stripe-shaped) light shielding layer (referred to as “black matrix”) BM is provided.
The lines and the transistors 11 are formed of a light shielding material and therefore decrease the ratio of an area actually contributing to display (referred to as “aperture ratio”) in a liquid crystal panel. However, in the case where the line extending across the picture elements (in this example, the scanning line 12) and the thin film transistors 11 are located within the reflection area Rf as shown in FIG. 21, the aperture ratio is improved and bright display is realized.
Patent Document 1: Japanese PCT National-Phase Laid-Open Patent Publication No. 2004-529396
Patent Document 2: Japanese Laid-Open Patent Publication No. 11-101992
Non-patent Document 1: M. R. Pointer, “The gamut of real surface colors,” Color Research and Application, Vol. 5, No. 3, pp. 145-155 (1980)